To make a polarizing sheet, generally a polarizing film that is obtained by absorbing or impregnating iodine or dichroic dyes in a monoaxially starched polyvinyl alcohol (PVA) film is used (hereafter, “PVA polarizing film”). Generally, transparent resins, such as triacetylcellulose, are used on one or both sides of the polarizing film as a protective layer or layers to make a polarizing plate. Such a polarizing plate is easily handled and is useful for secondary processing. Further, it is cheap and light.
The polarizing sheet is obtained by affixing a transparent resin sheet as a protective layer on both sides of a polarizing film (hereafter, a “polarizing sheet”). Generally, the film is a stretched polyvinyl alcohol film dyed with dichroic dyes. The polarizing sheet, which is obtained by a curving process, an injection process, or both, is used in polarizing lenses for sunglasses or goggles. Depending on the properties of the resin, for example, if the resin is an aromatic polycarbonate, the sunglasses or the goggles have superior impact resistance, as well as high heat resistance. If the resin is a polyamide, since it has superior stainability, one can obtain sunglasses or goggles that require various design characteristics.
For sunglasses and goggles that require impact resistance and heat resistance, the aromatic polycarbonate that is derived from bisphenol A is suitably used. However, since the aromatic polycarbonate has a large photoelastic constant, if the aromatic polycarbonate is curved to make a spherical or aspherical surface, such as in sunglasses or goggles, colored interference fringes easily arise by the retardation of the polycarbonate. As a result, the interference fringes cause problems such as deterioration in the appearance of articles and eyestrain.
Further, in a polarizing lens obtained by causing a polarizing sheet that uses an aromatic polycarbonate as a transparent sheet to curve to make spherical or aspherical surfaces, because of the uneven thickness of the aromatic polycarbonate polarizing sheet, distortion of images occurs. Therefore, the polarizing lens has problems in terms of causing deterioration in appearance (of articles) and eyestrain.
Regarding retardation that arises during the curving processes, an aromatic polycarbonate sheet that is used as a protective layer subjected to pre-extruding to make a large retardation to have colored interference fringes become invisible (hereafter, a “stretched polycarbonate polarizing sheet”) was known (Reference 1). Among various polarizing sheets, this sheet is used for articles that require an excellent appearance or that need to be beneficial to one's vision.
Further, for improving the function of a polarizing lens that is obtained by causing a polarizing sheet to curve, a polarizing lens that is obtained by causing a polarizing sheet to curve to form a spherical or aspherical surface, inserting the curved polarizing sheet into a mold, and injecting a transparent resin in the mold to produce the lens (hereafter, an “injection polarizing lens”), is known. A polarizing lens that uses an aromatic polycarbonate as a resin is also known (hereafter, “aromatic polycarbonate polarizing lens”) (References 2 and 3).
The aromatic polycarbonate polarizing lens is made by injecting an aromatic polycarbonate into a mold to fill the aromatic polycarbonate in the concave surface of the curved aromatic polycarbonate sheet. This brings about a benefit where the uneven thickness of the stretched polycarbonate sheet that is inserted in the mold disappears. Thus, even for lenses without focus refractivity, they are used in products that require particularly excellent impact resistance or appearance or that need to be beneficial to one's vision.
In lenses such as aromatic polycarbonate polarizing lenses that are obtained by inserting thermosetting resins or thermoplastic resins into molds, the shape and thickness of the molded lenses can be freely set by accordingly setting the shape of the surface of both sides of the mold and the distance between the two sides. Thus, based on the optical design, the shape and the distance between the two sides of the mold can be set so as to have the desired values of focus refractivity, prism-diopter, and image distortion.
The surface shape of the molded lens and the surface shape of the mold at the time of contact with the molded lens are generally identical. However, if a very high level of precision of the surface shape of the lens is required to compensate for a reduction in the thickness of the lens or a change in the surface shape, which are caused by shrinking of the volume when thermosetting resins or thermoplastic resins that are injected into molds solidify, the surface shape and the distance between the two sides of the mold should be adjusted accordingly.
The surface of the injection polarizing lens that is produced in this way is subject to further appropriate steps, such as forming a hard coat layer or an anti-reflection film, etc., and then polishing the rims of the lenses, drilling, screw fastening, etc., to fix the lens to the frame, thereby making sunglasses and goggles.
In the polarizing lens obtained by applying curving processes to the polarizing sheet to form a spherical or aspherical surface or the injection polarizing lens obtained by injecting an aromatic polycarbonate, etc., for the purpose of reducing the glare of the surface of the glass, the surface of water, etc., polarized light in the horizontal direction is cut. In addition, for the purpose of improving visibility or design, for example, an aromatic polycarbonate polarizing sheet colored grey, brown, or the like, is used to provide a desired color tone and transmittance.
To increase the degree of polarization of a polarizing lens, the amount of dichroic dye for dyeing a polyvinyl alcohol film is adjusted to a concentration at which the polarization component in the horizontal direction of light incident to the polarizing lens is almost all absorbed. And when the amount of the dichroic dye for dyeing the polyvinyl alcohol film is further increased, the polarization component in the perpendicular direction of light incident to the polarizing lens is also absorbed in a large amount. For a higher performing polarizing lens, a polarizing lens that shows decreased absorbance of the polarization component in the perpendicular direction of light incident in the polarizing lens, by using a dichroic dye that shows a higher dichroic ratio, is required.
Further, regarding the dichroic dyes for dyeing the polyvinyl alcohol film, not a single color, but dichroic dyes of several colors, are used. In this regard, by changing the amount of each dichroic dye for dyeing the polyvinyl alcohol film, a polarizing lens having a desired color tone and transmittance can be obtained. Further, a method to obtain a polarizing lens that has a color tone or transmittance of interest by dissolving the dyes in an adhesive layer or an aromatic polycarbonate sheet can be used. The method can control the color tone or the transmittance of an injection polarizing sheet by itself or in combination with the steps explained above.
Further, a method to obtain a polarizing lens that has a desired color tone or a desired transmittance by dissolving the dyes in an adhesive layer or an aromatic polycarbonate sheet can be used. The method can control the color tone or the transmittance of an injection polarizing sheet by itself or in combination with the steps explained above.
In a liquid crystalline material for a projection television that uses a polarizing film and color filters, a method was known for producing a color filter that has a polarizing function and a specific absorption function for absorbing wavelengths by using dichroic dyes and dyes that have low dichroic ratios. (Reference 4)